Conventionally, shot peening intensity has been evaluated using an arc height value obtained by using an almen strip. However, in quality management of the present state, in some cases, the shot peening intensity is managed using a peak value and depth of residual stress rather than the arc height value. This residual stress can be measured by an X-ray diffraction method (see, for example, Patent Literature 1). However, although the residual stress on a material surface can be measured in a non-destructive manner by the X-ray diffraction method, since a measurement region of a workpiece member has to be shaved when it is desired to obtain a residual stress distribution on the inside, a residual stress distribution of an actual product cannot be measured without breaking the product. The X-ray diffraction method is measurement in a shielded space for convenience of use of an X ray and there is a limit in the size of the workpiece member. There are many limitations in an evaluation method because it is difficult to make an X ray incident on a complicated-shaped object such as a gear.
When shot peening intensity is evaluated using the almen strip, it is impossible to evaluate which degree of force is applied to the surface of the workpiece member during shot peening processing. Therefore, an apparatus that detect shot peening intensity during shot peening processing using an AE sensor is examined (see, for example, Patent Literature 2). The apparatus described in Patent Literature 2 includes the AE sensor arranged in a shot (shot media) peened area. The AE sensor converts an elastic wave generated by shot projection into a high-frequency electric signal (an AE waveform). This apparatus detects a media flow rate and peened intensity of the shot using a peak value and the number of times of waveform generation of a voltage waveform obtained by converting the AE waveform.